The U.S. Treasury Department announced that the interest rate for Series I bonds will increase to 5.51% for the next six months, the highest fixed rate since 2006. The new rate will be effective from November 1st to April 30th, 2027, up from the previous rate of 4.26% which was valid until October 31st. This includes a variable component of 4.08% and a fixed component of 1.40%, with the fixed rate being higher than the 0.90% announced in April.